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Expression profiling during arabidopsis/downy mildew interaction reveals a highly-expressed effector that attenuates responses to salicylic acid.

Asai S, Rallapalli G, Piquerez SJ, Caillaud MC, Furzer OJ, Ishaque N, Wirthmueller L, Fabro G, Shirasu K, Jones JD - PLoS Pathog. (2014)

Bottom Line: By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1.By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells.Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA.

View Article: PubMed Central - PubMed

Affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom; Center for Sustainable Resource Science, RIKEN, Tsurumi, Yokohama, Kanagawa, Japan.

ABSTRACT
Plants have evolved strong innate immunity mechanisms, but successful pathogens evade or suppress plant immunity via effectors delivered into the plant cell. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis thaliana, and a genome sequence is available for isolate Emoy2. Here, we exploit the availability of genome sequences for Hpa and Arabidopsis to measure gene-expression changes in both Hpa and Arabidopsis simultaneously during infection. Using a high-throughput cDNA tag sequencing method, we reveal expression patterns of Hpa predicted effectors and Arabidopsis genes in compatible and incompatible interactions, and promoter elements associated with Hpa genes expressed during infection. By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1. Arabidopsis salicylic acid (SA)-responsive genes including PR1 were activated not only at early time points in the incompatible interaction but also at late time points in the compatible interaction. By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells. Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA. As this approach can be easily applied to host-pathogen interactions for which both host and pathogen genome sequences are available, this work opens the door towards transcriptome studies in infection biology that should help unravel pathogen infection strategies and the mechanisms by which host defense responses are overcome.

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Related in: MedlinePlus

Hpa development and scheme for aligning Illumina sequence reads.(A) Trypan blue staining in three-week-old Arabidopsis Col-0 plants at 1, 3 and 5 dpi with Hpa Emoy2 and Waco9. Black arrows indicate the parts in which HR cell death was observed. (B) Work-flow scheme to separate Illumina sequencing reads from Arabidopsis and Hpa.
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ppat-1004443-g001: Hpa development and scheme for aligning Illumina sequence reads.(A) Trypan blue staining in three-week-old Arabidopsis Col-0 plants at 1, 3 and 5 dpi with Hpa Emoy2 and Waco9. Black arrows indicate the parts in which HR cell death was observed. (B) Work-flow scheme to separate Illumina sequencing reads from Arabidopsis and Hpa.

Mentions: Arabidopsis Col-0 was inoculated with either the avirulent isolate Emoy2 (incompatible interaction) or the virulent isolate Waco9 (compatible interaction) of Hpa, and infected plants were harvested at 1, 3 and 5 days post-inoculation (dpi) prior to Illumina sequencing using EXPRSS [33]. Hpa haustoria are formed in both compatible and incompatible interactions till 1 dpi, and HR cell death is observed only in incompatible interactions [36]. HR was observed in Hpa Emoy2-inoculated leaves of Col-0 from 3 dpi, whereas no visible HR was observed at 1 dpi (Figure 1A). After Hpa Waco9 inoculation, extensive growth of intercellular mycelium was evident on leaves from 3 dpi, and then sporulation (conidiophores bearing conidiospores) was observed at 5 dpi (Figure 1A). In addition to the infectious stages, samples were taken from intact plants (0 dpi) and water-sprayed (mock-treated) plants as control samples for transcriptome analysis in Arabidopsis. Further, to evaluate the expression pattern of Hpa genes, samples were taken from conidiospores before inoculation. The experiment was carried out with three independent biological replicates.


Expression profiling during arabidopsis/downy mildew interaction reveals a highly-expressed effector that attenuates responses to salicylic acid.

Asai S, Rallapalli G, Piquerez SJ, Caillaud MC, Furzer OJ, Ishaque N, Wirthmueller L, Fabro G, Shirasu K, Jones JD - PLoS Pathog. (2014)

Hpa development and scheme for aligning Illumina sequence reads.(A) Trypan blue staining in three-week-old Arabidopsis Col-0 plants at 1, 3 and 5 dpi with Hpa Emoy2 and Waco9. Black arrows indicate the parts in which HR cell death was observed. (B) Work-flow scheme to separate Illumina sequencing reads from Arabidopsis and Hpa.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4199768&req=5

ppat-1004443-g001: Hpa development and scheme for aligning Illumina sequence reads.(A) Trypan blue staining in three-week-old Arabidopsis Col-0 plants at 1, 3 and 5 dpi with Hpa Emoy2 and Waco9. Black arrows indicate the parts in which HR cell death was observed. (B) Work-flow scheme to separate Illumina sequencing reads from Arabidopsis and Hpa.
Mentions: Arabidopsis Col-0 was inoculated with either the avirulent isolate Emoy2 (incompatible interaction) or the virulent isolate Waco9 (compatible interaction) of Hpa, and infected plants were harvested at 1, 3 and 5 days post-inoculation (dpi) prior to Illumina sequencing using EXPRSS [33]. Hpa haustoria are formed in both compatible and incompatible interactions till 1 dpi, and HR cell death is observed only in incompatible interactions [36]. HR was observed in Hpa Emoy2-inoculated leaves of Col-0 from 3 dpi, whereas no visible HR was observed at 1 dpi (Figure 1A). After Hpa Waco9 inoculation, extensive growth of intercellular mycelium was evident on leaves from 3 dpi, and then sporulation (conidiophores bearing conidiospores) was observed at 5 dpi (Figure 1A). In addition to the infectious stages, samples were taken from intact plants (0 dpi) and water-sprayed (mock-treated) plants as control samples for transcriptome analysis in Arabidopsis. Further, to evaluate the expression pattern of Hpa genes, samples were taken from conidiospores before inoculation. The experiment was carried out with three independent biological replicates.

Bottom Line: By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1.By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells.Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA.

View Article: PubMed Central - PubMed

Affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom; Center for Sustainable Resource Science, RIKEN, Tsurumi, Yokohama, Kanagawa, Japan.

ABSTRACT
Plants have evolved strong innate immunity mechanisms, but successful pathogens evade or suppress plant immunity via effectors delivered into the plant cell. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis thaliana, and a genome sequence is available for isolate Emoy2. Here, we exploit the availability of genome sequences for Hpa and Arabidopsis to measure gene-expression changes in both Hpa and Arabidopsis simultaneously during infection. Using a high-throughput cDNA tag sequencing method, we reveal expression patterns of Hpa predicted effectors and Arabidopsis genes in compatible and incompatible interactions, and promoter elements associated with Hpa genes expressed during infection. By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1. Arabidopsis salicylic acid (SA)-responsive genes including PR1 were activated not only at early time points in the incompatible interaction but also at late time points in the compatible interaction. By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells. Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA. As this approach can be easily applied to host-pathogen interactions for which both host and pathogen genome sequences are available, this work opens the door towards transcriptome studies in infection biology that should help unravel pathogen infection strategies and the mechanisms by which host defense responses are overcome.

Show MeSH
Related in: MedlinePlus